Screw nipple connection for electrodes



SCREW NIPPLE OOOOOOOOOOOOOOOOOOOOO ES Fi l e d J u l y 2 O l 9 59 EEEEEEEEE SCR EEEEEEEEEEEEEEEEEEEEEEEE CT RODES United States Patent O 3,048,433 SCREW NIPPLE CONNECTION FOR ELECTRODES Ernst Doetsch, Thornerstrasse 21, Nurnberg, Germany Filed July 20, 1959, Ser. No. 828,301 Claims priority, application Germany July 25, 1958 8 Claims. (Cl. 287-127) The present invention relates to a screw nipple connection and, more particularly, concerns an arrangement for securing a screw nipple connection with carbon and graphite electrodes for electric furnaces to prevent accidental loosening of such connection. A proper and safe screw nipple connection of carbon and graphite electrodes has prior to the present invention still remained an unsolved problem in spite of numerous efforts in this direction. This is particularly true with large electrodes.

In view of the great weight of such electrodes which, when connecting such electrodes to a strand frequently adds up to a total weight of several tons, the various factors tending to bring about a loosening of the connecting nipples yand thereby a detachment of the end surfaces of the electrodes adds up to such an extent that a proper current transfer of high amperes such as from 50,000 to 60,000 amperes, at the electrode tips will not be assured any longer.

For securing the screw nipple connections in connection with carbon and graphite electrodes for electric furnaces, the following methods have heretofore been employed: prior to screwing-in the nipple, the latter is coated with one of the known cements or binders on a tar, pitch, resin, or waterglass basis. When the binder or cement is heated, it cokes and the thus formed coke is supposed non-detachably Ito interconnect the nipple and the nipple box and, furthermore, to reduce the transfer resistance. With small electrode dimensions, this method is successful when the furnace conditions are favorable. However, with large electrodes, the difficulties will even increase for obvious reasons because the binder or cement layer ibetween the threads shrinks during the drying and coking of said binder or cement. Even though this shrinking amounts to a yfew tenth of a millimeter only in the individual threads, these amounts or clearances add up. Due to the high weight of the electrode, the nipple is pulled downwardly, the end Ifaces spread, and the current is forced to follow a path through the electrode boxes into the nipple. As a result thereof, due to the elimination of the end faces as contact surfaces, the nipple will be overloaded by approximately three times its normal load.

According to another heretofore known method, the nipple or box of the electrode is entirely or partially impregnated with tar or pitch. When subjected to heat, these inserted means sweat out and are supposed to seal the thread surfaces. This method has proved successful in many instances but, under certain furnace conditions, it has the drawback, particularly when the electrode is too quickly adjusted, that the impregnating means acts as liquid lubricant and thus directly favors the loosening of the connection if it does not coke at the proper time. The same situation is encountered when employing tar pins. In `such an instance, the nipple is additionally weakened by large Ibores. This disadvantage is also encountered with meltable carbon containing substances in cavities of the ends of the electrodes or the nipple.

According to another frequently practiced procedure, the screw nipple connection is secured by means of graphite pins which are `driven laterally through the box into the nipple into pre-drilled bores thereof. However, experience has shown .that the tensions caused by the graphite pins which are subjected to high tensional stress bring about tears in the electrode box as a result of which the ICC tension of the entire threaded box is loosened thereby unavoidably causing a loosening of the thread portion.l

It is, therefore, an `object of the present invention to provide a screw nipple connection yfor carbon and graphite electrodes of the above mentioned general type, which will overcome the drawbacks outlined above.

It is also an object of this invention to provide a screw nipple connection of the above mentioned general type, in which the pressed-in cement or binder used for the connection will be prevented from detaching itself from the electrode walls.

It is also an object of the invention to provide a connection of the type set forth in the preceding paragraph, `which will facilitate the escape of the gases produced during the coking.

It is still another object of this invention to provide a screw nipple connection for carbon and graphite electrodes, 'which will facilitate the introduction of binding or cement material into .the spaces between the threaded nipple and the box wall to thereby increase the friction counteracting any possi-ble loosening or detachment of the connecting elements from each other while simultaneously greatly improving the current transfer.

These and other objects and advantages will appear more clearly fromthe following specification in connection with the accompanying drawings, in which:

FIG. l represents -a longitudinal section through a screw nipple connection according to the present invention.

FIG. 2 is a longitudinal section similar to that of FIG. 1 through a modified screw nipple connection of the in- 'vention FiG. 3 illustrates an end face of the screw nipple of the invention with depressions provided therein in conformity with the invention.

FIG. 4 is a longitudinal section through still another modied screw nipple connection of the invention.

FIG. 5 is a section along the line V--V of FIG. 4.

General Arrangement According to the present invention, the screw nipple connection with carbon and graphite electrodes for electric furnaces is secured against loosening by providing the end faces of the threaded nipple and also the bottom of the threaded boxes with a plurality of cylindrical semispherical or similarly shaped depressions of a diameter and depth of from l to 2 centimeters, said depressions being distributed over the entire end surfaces. Furthermore, in conformity with the present invention, a thin bore having a diameter of from 2 to 3 millimeters is provided in the wall of the threaded boxes at the level of the bottom of the threaded box. It is through this thin bore that after the threaded connection has been established, a cement material on a water glass or synthetic resin basis is pressed under high pressure from the outside into the free spa-ce between the screw nipple and the threaded box. This cement material will harden by itself and will not soften anymore prior to the coking so that at each end of the screw nipple there will form a disc with a plurality of studs extending into the nipple end face and into the bottom of the box so that a rotation of the threaded nipple will be prevented by the locking eifect of said studs.

In order to allow the air in the hollow chambers to ,escape therefrom, the electrode end faces` are provided with a non-rectilinear groove.

The screw nipple may in a manner known per se be provided with a longitudinal bore whereby the cement material may be introduced merely through the bore of the superimposed electrode because the cement material will, through said longitudinal bore, pass into the lower free chamber and fill the same. In this instance, the air can escape through the bore in the lower electrode. The

longitudinal bore in the nipple will then likewise be filled with cement material.

The nipple may furthermore be locked against rotation by repeatedly interrupting the thread of the nipple and of the box by grooves which may extend in longitudinal direction or at an angle thereto. The grooves have to be designed so that when screwing together the nipple and the electrodes, the grooves in the nipple thread will be located opposite the grooves in the thread of the box or will intersect the same.

For purposes of increasing the electric conducti-vity of the cement material, the cement material may have added thereto metals or metal carbides.

In order to prevent the pressed-in cement material from shrinking whereby the contact would become worse in view of the detachment of the cement material from the electrode wall, it may be advisable to add to the cement material a gas driving means such as ammonium bicarbonate whereby the cement material will be firmly pressed against all electrode surfaces. The escape of the gases which may be produced during the coking can be facilitated by the arrangement of capillaries in the threaded box.

By specially shaping the non-supporting flanks of the thread, it is also possible to facilitate the introduction of the cement material into the interstices or gaps between the screw nipple and the box wall. The friction counteracting the loosening will in this way be increased considerably and the current transfer will become considerably more uniform while local heat developments which might cause tensions and tears in the box will be avoided.

Structural Arrangement Referring now to the drawing 4in detail, the screw nipple connection shown in FIG. l comprises an electrode a and an electrode b which are interconnected by a conioal screw nipple c. The end faces of the screw nipple c and the bottom of the threaded box are provided with a plurali-ty of cylindrical depressions d. At the level of the bottom of the threaded box, both electrodes have a thin bore e through which from the outside a self-hardening cement material is pressed under high pressure into the free space or gap between the screw nipple c and the threaded box. The free space or gap between the nipple and the box in the lower electrode b has been left free merely for a clearer illustration, and it is, of course, to be understood that also this free space will be filled with self-hardening cement material. After the cement material has hardened, a loosening of the connection will not be possible any longer in view of the connection by the locking effect of the studs engaging the depressions d and pertaining to the discs f formed by the pressed-in cement material.

Referring now to FIG. 2, the screw nipple connection shown therein likewise comprises the two electrodes a and b which are interconnected by a screw nipple c. However, in contrast to the arrangement of FIG. 1, the depressions d in the end faces of the nipple and in the bottom of the threaded box are designed semi-spherically. Also with the arrangement of FIG. 2, thin bores e are provided in the electrodes a and b at the level of the bottom of the threaded box. The arrangement of FIG. 2 differs from FIG. l furthermore in that the screw nipple lis provided with a thin longitudinal bore g. As will be evident from FIG. 2, the cement material is in this instance underhigh pressure pressed from the outside through the thin bore e of the electrode a into the free space or gap between the nipple and the box. The cement material passes through the longitudinal bore g also into the free spaces or gaps of the electrode b. After the cement material has hardened, also in this instance discs will form between the end surface of the nipple and the bottom of the box. These discs f will likewise,

through the studs engaging the depressions d, prevent the nipple from rotation. The bore e of the electrode b allows the air to escape from the intermediate spaces.

FIG. 3 shows the end face of the screw nipple with the depressions d.

Referring now to FIG. 4, the screw nipple connection shown therein comprises an electrode a and an electrode b which are firmly connected to each other by means of the screw nipple c. In order to prevent the connection from loosening, semi-spherical depressions are provided in the end surfaces of the screw nipple and in the bottom of the threaded box. These depressions d are filled with a self-hardening cement material which is pressed at high pressure from the outside through bores e into the free spaces between the nipple and the box. In order additionally to secure the connection, the thread of the nipple and of the box is provided with a plurality of longitudinal grooves h which are likewise filled with cement material. The longitudinal grooves must be so designed and arranged that when screwing together the various parts, the grooves of the nipple will be opposite the grooves in the box so that the pressed-in cement material will create a plurality of studs which, together with the disc f between the nipple end face and the bottom of the box, will prevent the nipple from rotating.

FIG. 5 showing a section along the line V-V of FIG. 4, likewise indicates the electrode a and the threaded nipple c as well as the longitudinal grooves h filled with cement material, said grooves being provided in the thread of the nipple and the box.

The screw nipple connection according to the invention does not only prevent the connected parts from getting loose and detaching themselves from each other, but also assures a good current transfer at the end faces of the screw nipple.

It is, of course, to be understood that the present invention is, by no means, limited to the particular construction shown in the drawings but also comprises any modifications within the scope of the appended claims. While various self-hardening binding cements may be employed for the above purpose, a binding cement composed primarily of graphite powder and synthetic resin has proved highly satisfactory.

What I claim is:

1. In combination: a first electrode, a second electrode having one end portion in engagement with an end portion of said first electrode, each of said end portions of said electrodes being provided with a threaded bore, a threaded nipple threadedly engaging said threaded bores and interconnecting said end portions of said electrodes, the end faces of said nipple and also the electrode surfaces respectively facing said end faces of said nipple being provided with depressions, and a self-hardening cement filling said depressions in said nipple and said electrodes, thereby anchoring Said electrodes and said nipples relative to each other and preventing rotation of said electrodes and said nipples with regard to each other.

2. In combination: a first electrode, a second electrode having one end portion in engagement with an end portion of said first electrode, each of said end portions of said electrodes being provided with a threaded bore, a threaded nipple threadedly engaging said threaded bores and interconnecting said end portions of said electrodes, the end faces of said nipple and also the electrode surfaces adjacent to said end faces of said nipple being provided with depressions, at least one of said end portions of said electrodes being provided with a passage extending from the outside thereof to the adjacent depressions, and a self-hardening cement filling said passage and said depressions, thereby anchoring said electrodes and said nipples relative to each other and preventing rotation of said electrodes and said nipples with regard to each other.

3. An arrangement according to claim 2, in which the depressions in the end faces of said nipple are interconnected by a passage extending through said nipple and filled with the self-hardening cement.

4, In combination: a first electrode, a second electrode having one end portion in engagement with an end portion of said first electrode, each of said end portions of said electrodes being provided with a threaded bore, a threaded nipple threadedly engaging said threaded bores and interconnecting said end portions of said electrodes, the thread of said nipple and the thread of said bores respectively being provided with grooves extending in longitudinal direction of said nipple and intersecting said thread of said nipple and of said bores, said grooves being filled with a self-hardening cement whereby said electrodes and said nipple are anchored to each other and prevented from rotating relative to each other.

5. In combination: a first electrode, a second electrode having one end portion in engagement with an end portion of said first electrode, each of said end portions of said electrodes being provided with a threaded bore, a threaded nipple threadedly engaging said threaded bores and interconnecting said end portions of said electrodes, the thread of said nipple and the thread of said bores respectively being provided with grooves extending in longitudinal direction of said nipple and intersecting said thread of said nipple and of said bores, said grooves in said nipple and said grooves in said electrodes being in alignment with cach other and being filled with a selfhardening cement whereby `said electrodes and said nipple are anchored to each other and prevented from rotating relative to each other.

6. A method of securing to each other the adjacent end portions of electrodes provided with threaded bores and interconnected by a threaded nipple, which includes the steps of: providing the end faces of said nipple with depressions and also those portions of said electrodes which face said end faces of said nipples, drilling a bore through at least one of said electrodes to said depressions, and introducing through said bore into said depressions binding substance of a self-hardening nature.

7. In combination: a first electrode, a second electrode having one end portion in engagement with an end portion of said first electrode, each of said end portions of said electrodes being provided with a threaded bore, a threaded nipple threadedly engaging said threaded bores and interconnecting said end portions of said electrodes, the end faces of said nipple and also the electrode surfaces adjacent to said end faces of said nipple being provided with depressions, at least one of said end portions of said electrodes being provided with a passage extending from the outside thereof to the adjacent depressions, the thread of said nipple and the thread of said bores being provided with grooves extending from said passage in longitudinal direction of said nipple so as to intersect windings of the thread of said nipple, and a self-hardening cement filling said passage and said depressions and said grooves, thereby anchoring said electrodes and said nipple relative to each other and preventing rotation of said electrodes and said nipple with regard to each other.

8. In combination: a first electrode, a second electrode having one end portion in engagement with an end portion of said first electrode7 each of said end portions of said electrodes being provided with a threaded bore, a threaded nipple threadedly engaging said threaded bores and interconnecting said end portions of said electrodes, and a selfhardening cement anchored in said end portions and said threaded nipple to thereby prevent rotation of said electrodes and said nipple relative to each other, said selfhardening cement containing a gas driving substance for aiding the electric conductivity of the connection of said electrodes at their connecting points.

References Cited in the file of this patent UNITED STATES PATENTS 1,850,515 Peitz Mar. 22, 1932 2,093,390 Wyckoi Sept. 14, 1937 2,158,845 Ayer May 16, 1939 2,510,230 Johnson June 6, 1950 FOREIGN PATENTS 287,703 Switzerland Apr. 16, 1953 472,856 France Aug. 16, 1914 

